Malignant tumors of the head and neck are particularly destructive and difficult to deal with. Surgical treatment alone is a destructive method of treatment, but combined with chemotherapy and radiotherapy treatment has been improved. Still, radiotherapists have long desired a means of solving the problem of the concomitant injury to normal adjacent tissue while destroying cancerous tissue with x-ray. Recently, a new experimental radioprotective compound known as WR-2721 (S-2-(3-Aminopropylamino) ethyl phosphorothioic acid) was found to provide good differential radioprotective effects between normal and malignant tissues and was well tolerated by humans. The purpose of this study is to determine whether WR-2721 can be effective in lessening the damage to the rat parotid gland caused by high doses of x-radiation. The protective effects of the drug will be evaluated by studies of salivary flow, amylase content, synthetic ability and morphologic appearance during periods ranging from the first week to 3 months following irradiation with 1600, 3200 and 6400 R.